I remember many summers locked in my bedroom, writing deep into the night, scribbling on page after page in a notebook (yes, I was a pretty geeky kid). It was a thrill. I loved just letting out the words onto paper. However, I ended up with a lot of great beginnings, a lot fewer middles, and almost no endings.
Why? I got stuck. I had no idea what to write next. Because I had no plan.
As much as I adore inspiration and creativity, over the years I have come to be convinced that in order to write, write well, write consistently – to complete a full-length novel at a steady pace – you ought to have a chapter-by-chapter plan. It’s OK to digress, it’s OK to go off on some sub-plots, it’s OK to weave in more detail, but if you have no plan at all you’re a lot more likely to end up with more loose ends than you can neatly wrap up.
1) Have a chapter-by-chapter plan, and a broader book-by-book plan if writing a series.
2) Keep a list on hand with some details you know you're likely to forget, like the age and appearance of various characters, historical details, places, stuff like that. It's important if you write long books with lots of characters and background. Silly as it is, you can forget what you wrote yourself. Mistakes happen all the time - not long ago, in a book by a serious, professional author that was actually printed by a good publishing house, I spotted that the main character has green eyes in one chapter and brown eyes in another. Obviously the editor had been sloppy.
3) Have a number-of-words-per-sitting writing goal. For me this means the following: if I sit down to write, and have no interruptions (and with three young kids, you can bet I get interrupted a lot), I aim to have written a 1,000 words by the time I get up. No less, and preferably no more - I can churn out 2K words in one sitting if inspiration hits, but I've found this is a pretty fast way to burnout. Once I've done my 1,000 words a day, I'm free to dedicate time to other things, like reading out a chapter of Winnie the Pooh or looking up recipes for homemade ice-cream.
4) Discipline. While writing, don't let yourself be tempted to slack off to check your email "for just a second", give someone a Like on Facebook, etc. Such things throw you off course and it's a lot harder to get in pace later.
Let's sum it up: have a plan; have a consistent day-to-day working goal; stick to it until you're done.